Demonstration of breaking the Java enum singleton pattern:
public enum MySingleton {
INSTANCE;
MySingleton() {
System.out.println("Should happen only ONCE!");
}
}Requires Java JDK version 8 or higher.
$ java -version
openjdk version "17.0.1" 2021-10-19
OpenJDK Runtime Environment (build 17.0.1+12-Ubuntu-120.04)
OpenJDK 64-Bit Server VM (build 17.0.1+12-Ubuntu-120.04, mixed mode, sharing)
$ ./gradlew -q run
Should happen only ONCE!
class test.MySingleton.INSTANCE/0x18b4aac2 @ class loader jdk.internal.loader.ClassLoaders$AppClassLoader@30946e09
Should happen only ONCE!
class test.MySingleton.INSTANCE/0x6bc7c054 @ class loader java.net.FactoryURLClassLoader@2a139a55
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